In container transport systems, preforms made from plastics, such as for example polyethylene terephthalate (PET), polypropylene (PP) etc., are moulded into containers such as for example bottles, and are subsequently labelled, filled, packaged etc. To this end, the preforms transported through the container treatment system along a transport path are heated in a heating device, so that they can then be expanded and stretched into plastic containers in a stretch blow moulding apparatus by means of a stretch blow moulding process. Subsequently, the plastic containers are transported by a transport system to further treatment apparatus such as for example a cleaning device, a labelling device, a filling device, a sorting device, a packaging device, etc.
The transport systems used for this purpose are so-called neck-handling systems, in which a retaining clamp of the transport system grips above or below a support ring of the preforms or the expanded container, in order to hold the respective preform or expanded container on the transport system and to transport it in this way through the container treatment system. Usually, the retaining clamps are fastened in a star shape around a driving shaft, so that this is also referred to as a transport star. Due to such an arrangement around the driving shaft, the retaining clamps generally carry out a circular or at least approximately circular movement. In this respect, rigid transport stars, sliding transport stars and partial-delay transport stars are distinguished. In the case of rigid transport stars, the retaining clamps rigidly follow the circular path or the transport path determined by the transport star. In the case of sliding transport stars, the retaining clamps can partially leave the transport path determined by the transport star. In the case of partial-delay transport stars, the retaining clamps can also leave the pitch on the transport path determined by the transport star.
However, what all of these conventional transport systems have in common is that all the retaining clamps follow the same travel-time profile and the transport path is substantially circular. This is in particular disadvantageous in a transport system between a heating unit for preforms and a stretch blow moulding unit in a case where large preforms are to be heated. In such a case, the heating unit has to run more slowly than in the case of smaller preforms, whereas the subsequent stretch blow moulding unit can run at the same speed for both preform sizes, since in the case of large preforms, for example, only every other blow mould of the stretch blow moulding unit is loaded with the heated large preforms.
EP 1 645 340 A1 describes a sorting device and a conveying device for piece goods, wherein retaining devices for holding the piece goods on individual transport units are arranged, which can be individually controlled, so that they can be carried from a loading place to a selectable delivery place. By this means, piece goods held on the retaining devices can be transported along a substantially circular transport path and can be diverted and thus channeled by the latter to side transport paths as a function of the type of piece goods held. The side transport paths are designated for special types of piece goods, in order to carry the piece goods to the delivery place intended for them. Such a sorting device and conveying device, however, continues to adhere to a fixed travel-time profile of the transport units on the transport path, simply because it doesn't need another one, and thus approximately corresponds to the above-mentioned sliding star. Therefore, the problem mentioned above as an example, namely that of changing from small preforms to large ones and vice versa, cannot be solved.
DE 41 33 114 A1 shows a conveyor system for piece goods such as bottles, containers and the like, which has a conveying path formed as a long stator motor with stationary electric/electronic components and brushless rotors for conveying piece goods. The conveying path carries the piece goods past or through several treatment stations arranged one after the other. Because its entire conveying path is formed as a long stator motor, such a conveying system is clearly more expensive to procure and to maintain than the above described transport stars.
It may therefore be desirable to provide a transport unit and a transport method for a container treatment system, which enable the transport process to be carried out independently by two different container treatment apparatus of a container treatment system in a cost effective manner.